Discussion on the emulsification problem of alkali solution in liquefied gas desulfurization

1. To what extent is the emulsification problem of the sodium hydroxide solution used in the liquefied gas desulfurization process serious? Can neither the improved Merolox process nor the fiber membrane process solve this issue? This is indeed a serious problem; the backmixing of disulfides it causes has a significant impact on the total sulfur content in liquefied gas, resulting in the liquefied gas failing to meet quality standards ； The improved processes basically involve adding solvent oil for back-extraction, utilizing the principle of like dissolves like to separate disulfides. 2. The emulsification of disulfides in alkaline solutions may be due not only to the small density difference, but also to the synergistic effect of organic substances such as thiol compounds and catalysts present in the alkaline solution, which leads to enhanced emulsification of the disulfides Our experimental tests showed that when dimethyl disulfide is mixed with alkali solutions of different concentrations and shaken, the emulsification effect is not very good; after about 2 hours, the oil and water separate completely, and the higher the concentration of the alkali solution, the faster this separation occurs. Using oils with low sulfur content for extraction can solve this problem, after all, the alkaline solution is in an inorganic phase, and sodium thiolate is also in an inorganic phase. 3. Disulfides have a certain solubility in alkaline solutions; if the emulsified disulfides are completely removed, will the dissolved disulfides affect the reuse of the alkaline solution? Is it still necessary to use the subsequent hydrogenated reformate for extraction, even after the emulsified disulfides have been completely removed? Extract it; this will solve the emulsification problem.

Then, if a method other than extraction is used to separate the emulsified disulfides from the recycled alkaline solution – in other words, if the emulsified disulfides or other oil phases are completely removed – can the resulting alkaline solution be used directly again?

It can be reused directly. This is the general process for regenerating alkaline solutions: either solvent oil is used for extraction or the disulfides are separated in gaseous form, so as to prevent the alkaline solution from mixing back together.

What is the approximate content of emulsified disulfides in the circulating alkaline solution during actual production?

No monitoring has been conducted, but the disulfides in the alkaline solution after extraction have little impact on the quality of liquefied gas. On the contrary, liquefied gas extracted without the use of solvent oil has a relatively high total sulfur content. In fact, the process of extraction using oil is similar to the re-mixing of liquefied gas; it follows the same principle of like dissolving in like.

Could we solve this problem by thinking in a different way? Since disulfides emulsify in alkaline solutions, then if they are not left in that alkaline solution after formation, they won’t emulsify, right? Therefore, the technology we have developed allows the disulfides to go directly into the exhaust gases, with the exhaust gases being subsequently treated to render them harmless. There is thus no back-extraction of disulfides by liquefied gas, and the process no longer requires an oxidation tower or solvent oil for back-extraction. In terms of results, liquefied gas achieves deep desulfurization, and alkaline slag is also eliminated!